When a caller calls an emergency number, e.g. 911 (E911), the call is routed to a public safety answering point (PSAP). In some jurisdictions, regulatory agencies require that the caller's telephone number/callback number and/or precise physical location referred to as an Emergency Location Identification Number (ELIN), be automatically provided to the PSAP. The information in the ELIN is used to locate the caller and to call back the caller should there be a disconnect.
A caller identification (i.e., telephone number and ELIN) may be delivered to the PSAP either in-band (e.g., using DTMF signaling) or out-of-band (e.g., using ISDN signaling) depending on the type of trunk circuit employed. Normally, for residential callers, calling party number (CPN) is sufficient for PSAPs. In some cases, the ELIN is substituted with earth coordinates or geo-positional synchronous (GPS) data or other geodetic data.
Digitally encoded voice communications that are transmitted over a network, using what is typically referred to as voice over Internet protocol (VoIP) may originate anywhere and possibly, follow a circuitous route to a distant destination for far-end hop-off to a public service telephone network (PSTN). Thus, placing an E911 call over a VoIP enabled telephone network may be a problem. Currently, it is not possible in an IP network (e.g., VoIP) to identify the source location of an originating device whose destination is 911 (or other emergency number) and to route the call to the proper PSAP jurisdiction (or other designated jurisdiction).
A database called an automatic location information (ALI) database is associated with one or more PSAPs. The ALI database is generally part of a database management system having a database server through which the ALI database is queried. The ALI database contains records that associate telephone numbers (e.g., CPNs) with locations. When a telephone call is made to 911, the ALI database is queried for location information. The query may contain the telephone number associated with the telephone that made the 911 telephone call. In response to the query, the ALI database passes geographic location information back to the PSAP. This information is used to route the telephone call to the proper PSAP and is also made available to the 911 operators located at the PSAP.
Currently, 911 calls are routed on multi-frequency (MF) trunks through 911 tandems. Each of these tandems includes a separate 911 ALI database for the area that it serves. Currently, Internet Protocol (IP) devices are available to allow a customer to utilize an IP telephone and still have advanced calling features such as call-waiting and call-forwarding. However, when the IP device is moved to a different IP port, either inside or outside of the geographic region being served by the original 911 tandem, there is no way to associate the customer information (e.g., geographic location) with the 911 telephone call in order to route the telephone call to the PSAP or to provide information to the 911 operator.